Much work has been done in the field of photopolymerizable compositions to increase the speed of these materials. However, many of the well-known photoinitiators or photoinitiator systems limit the applicability of photopolymerizable compositions because they are activatible primarily by radiation in the ultraviolet region of the spectrum. The availability of reliable, relatively inexpensive lasers which emit in the visible region of the spectrum has made it desirable to develop initiator systems for photopolymerizable materials which are sensitive to visible radiation. Such applications include the use of supported photopolymerizable layers for preparing graphic arts films and proofs, printing plates, photoresists, holograms and the like such as are disclosed in the following U.S. Patents: Alles, U.S. Pat. No. 3,458,311; Celeste, U.S. Pat. No. 3,469,982; Chu et al., U.S. Pat. No. 3,649,268; Haugh, U.S. Pat. No. 3,658,526; Chen et al., U.S. Pat. No. 4,323,637; Dueber, U.S. Pat. No. 4,162,162; Bratt et al., U.S. Pat. No. 4,173,673; Cohen et al., U.S. Pat. No. 4,282,308; and Dueber, U.S. Pat. No. 4,613,560. In addition these lasers can be used in output devices for electronic imaging systems.
A large number of free-radical generating systems have been utilized as visible sensitizers for photopolymerizable compositions. Redox systems, especially those involving dyes, e.g., Rose Bengal/2-dibutylaminoethanol, have been used. Photoreducible dyes and reducing agents such as those disclosed in U.S. Pat. Nos. 2,850,445; 2,875,047; 3,097,096; 3,074,974; 3,097,097; 3,145,104; and 3,579,339; as well as dyes of the phenanzine, oxazine, and quinone classes have been used to initiate photopolymerization. Initiation by ionic dye-counter ion complexes and by cationic dye-borate anion complexes is described in Gottschalk et al., U.S. Pat. Nos. 4,772,530 and 4,772,541. A useful discussion of dye sensitized photopolymerization can be found in "Dye Sensitized Photopolymerization" by D. F. Eaton in Adv. in Photochemistry, Vol. 13, D. H. Volman, G. S. Hammond, and K. Gollinick, eds., Wiley-Interscience, New York, 1986, pp. 427-487.
Dueber, U.S. Pat. No. 4,162,162, as well as U.S. Pat. Nos. 4,268,667 and 4,351,893, discloses selected sensitizers derived from aryl ketones and p-dialkylaminoaldehydes. Dueber and Monroe, U.S. Pat. No. 4,565,769, discloses photopolymerizable compositions containing polymeric sensitizers which are activatible by visible radiation. Baum and Henry, U.S. Pat. No. 3,652,275, discloses selected bis(p-dialkylaminobenzylidene)ketones as sensitizers to enhance the efficiency of hexaarylbiimidazole initiator systems in photopolymerizable compositions. Cohen, U.S. Pat. No. 3,554,753, discloses selected carbocyanine dyes as sensitizers of hexaarylbiimidazole containing imaging systems.
The use of visible sensitizers is crucial for the preparation of holograms in photopolymerizable and photocrosslinkable systems such as are disclosed in Haugh, U.S. Pat. No. 3,658,526. While suitable sensitizers are available for use in these systems, there is a need for other sensitizers which closely match the spectral laser outputs used, particularly in the regions extending into the yellow, red and infrared portions of the spectrum.
Lasers are also being used to image photopolymerizable resists during the manufacture of printed circuits, optical storage media and the like. While UV and some visible lasers can be used in current systems, there is a need for extended sensitivity photoresists so that high resolution images can be prepared to survive the rigorous processing conditions encountered during manufacture of high quality printed circuits.